PSI - Issue 75

Luca Corsaro et al. / Procedia Structural Integrity 75 (2025) 140–149 Luca Corsaro , Francesca Curà, Raffaella Sesana / Structural Integrity Procedia (2025)

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an appreciable temperature increment was early detected during the bending fatigue tests. Subsequently, the thermal parameter (integrated area) corresponding to each ΔT emp profile was calculated in accordance with Section 2.1, as illustrated in Fig. 4(b). The analysis of Fig. 4 (a) shows that the C45 induction hardened gears exhibited the same thermal behaviour up to a certain tested load, since a significant temperature increment was clearly detected at the highest pulsating forces. This behaviour can be observed in the analysis of the evolution of the thermal parameters (see Fig. 4 (b)), where an abrupt change was obtained as a result of the different intrinsic dissipations generated by the gear. Similar results are reported in Fig. 5 for the 20MnCr5 carburized gear. More in detail, the ΔT emp profiles obtained acquiring the bending fatigue tests are illustrated in Fig. 5 (a), while the corresponding thermal parameters evolution (integrated area evolution) is shown in Fig. 5 (b). In order to appreciate the thermal variations on the basis of the tested load, a number of cycles equal to 100000 was adopted during the bending fatigue tests. In this case, the variations in the thermal response as a function of the applied load (ΔT emp profiles in Fig. 5 (a)) were less pronounced if compared with those obtained in case of C45 induction hardened gear (see Fig. 4 (a)). In any case, the examination of the thermal parameters evolution (see Fig. 5 (b)) confirmed an incremental trend based on the loading conditions, clearly emphasised for the last tested loads.

Fig. 6. Fatigue limit estimations: (a) C45 induction hardened gear; (b) 20MnCr5 carburized gear. Fig. 6 illustrates the fatigue limit estimations obtained from the thermal parameters presented in Fig. 4 and Fig. 5. The TCM analysis was conducted with the specific aim of evaluating the F pn ∾ value (see Section 2.1). The thermal parameters evolution (integrated area) was approximated by linear approximating curves on the basis of the pulsating force adopted during the fatigue test by means of an iterative and automatic process. Then, the corresponding intersection between the two approximating curves allowed the estimation of the F pn ∾ of the gear, 20745 N for the C45 induction hardened gear and 13678 N for the 20MnCr5 gear respectively. The F pn ∾ estimated with the proposed approach was used to calculate the stress that leads to bending failure (σ FP ) according to the formula in ISO 6336-3 (2019) (Method B). The computation (see Section 2.2) requires the geometry of the gear (m n and b, see Table 1) and the stress correction factors (Y s and Y f , see Table 1). The assessment was subsequently improved by taking into account the 1% failure probability and the correction coefficient for STBF tests (Stahl (1999)). The final σ FP results are summarized in Table 2. The σ FP obtained considering the ISO 6336-3 (2019) computations (σ FP-ISO ), the Staircase M ethod (only for the 20MnCr5 gear, σ FP-SC ) and the Thermographic Method (σ FP-TCM ) are presented for both tested gears (C45 induction hardened gear and 20MnCr5 carburized gear). From the